220 HISTORY OF BOTANY 



problem about the same time, and their investigations 

 showed that the exhalation of carbon dioxide must be 

 distinguished from the inhalation of oxygen, since an 

 animal such as a frog could live and give off carbon 

 dioxide for some hours in the absence of oxygen gas. 

 Conversely, De Saussure, in 1804, found that a cactus, 

 though supplied with oxygen, gave off no carbon dioxide. 

 De Saussure's experiments were reinvestigated by 

 Deherain in 1874, with the result that oxalic acid was 

 discovered in large amounts in the tissues. It was 

 obvious that, in this case at all events, respiration was 

 not a simple combustion of carbon. 



The trend of research, in short, went to show once 

 more that the whole performance was intimately con- 

 nected with the protoplasm and the instability of its 

 constituents. In 1875 Pfliiger had put forward a hypo- 

 thesis that protoplasm had the power of auto-decomposi- 

 tion ; that oxygen became incorporated in it intramolecu- 

 larly and so increased its " lability " or instability, the 

 final result being an " explosion/' Detmer, in 1883, 

 adopted this idea and suggested " that the primary 

 source of the energy developed in living organisms consists 

 in the splitting up of highly complex labile compounds, 

 the decomposition products of which subsequently 

 become oxidised, carbon dioxide and water being the 

 ultimate products." 



These ideas received considerable support from the 

 researches of Pasteur on fermentation. As you already 

 know, he had shown that many yeasts and other micro- 

 organisms could exist in the absence of free oxygen, and 

 indeed that several could not exist in its presence ; 

 these forms he described as " anaerobic. " It was also 

 shown by Hoppe-Seyler, in 1887, that the products due 

 to the activities of putrefactive bacteria differed according 

 as to whether the putrefactive process went on in the 

 presence or absence of oxygen. In the former case 

 oxygen, carbon dioxide, water, and ammonia were formed ; 



